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RV-7A Cooling issues, Sam James Cowl

F

float208

Well Known Member
Anyone have a Sam James cowl and had cooling issues? What were the fixes in a nutshell that helped lower the temps??

RV-7A
Oil at 24/24 210-220
OAT 85
CHT 398 on #1,2,4 415 on #3

Feedback on CHT cooling? the only things I can think of right now is cutting the cowl scoop on the bottom back a bit to create a better exit, and siliconing the plenum (wanted to wait to inspect after the first flight). Any luck with trimming the cowl bottom? If so how far did you trim. Photos would be great!!

Thanks in advance!
 
There have been a few that have, myself included. I'm not sure the cowl is to blame, though...it seems that just as many have no cooling issues. Plus, consider that Van's cowl users have both cooling issues and a lot of them don't have cooling issues. To be frank, I think there are too many factors to point to any single cause of problems, like the cowl.

My setup is that I have the Sam James shorty cowl with the SJ plenum. I have an ECI 0-360, carbed, with Nickel Cerminil cylinders. I also have piston skirt squirters and dual P-Mags. Before last year I had the standard Niagra 7-row oil cooler. Now I have the 10 row cooler, which seemed to have dropped my oil temps about 15 degrees (F).

The cylinders, skirt squirters, electronic ignition and having an -A model RV all can negatively effect cylinder and oil temps. I'm currently working with a couple other RV'ers on measuring cowl pressure differentials, because we believe that the airflow isn't optimal. So far, signs are pointing to the SJ cowl as having poorer air flow than the Vans, but I'm guessing that's the trade off for Sam James' claimed extra speed.
 
Yes, I had similar numbers on my -7. Had to step climb, but once at speed and alt things settled in ok. 390-405CHt, 205-210 oil. And if I slowed down the oil temp shot to 220 and things got interesting. So

I trimmed the lower cowl outlet so that it ended at the firewall. I previously left it longer ~5/8 to help straighten outlet flow. This dropped temps to 380-390cht's and 190-200 oil. Acceptable, But I wanted more

This spring I made an internal cowl outlet mod which consisted of a baffle to add a radius upper surface as the air leaves the cowl/firewall interface. This seems to have dropped temps to 350ish in cruise and oil is 190. The big test for me was at the Llano race last weekend. I was able to run WOT, 2600 rpm and oil never got above 192, CHT under 375 for the complete race. Once I slowed and landed oil temp went to 205. My next move will be to start closing down the outlet to reduce drag at race speed. Might make it cockpit adjustable for cooling reasons.
 
Brian,

Can you post pictures of your latest Mod?

I have a 7A with O-360 and the James cowl. My oil temp was a bit high, but it dropped 10 or 15 deg with the addition of louvers (the cooler exit is right above the louver. CHTs are still higher than I would like and can hit 400 when leaned, so i would like to make some improvement there. Cowl is already flush with the firewall and I have heard others got benefit from cutting it back further.
 
I don't really have any good pics when finished. but here is a during construction pic. It's just a simple piece of .025 AL screws adel clamped to the engine mount. The lower edge is a radius and screwed to the firewall lip.
aviation2012107.jpg
 
Hey Brian, I'm in the middle of my annual condition inspection and plan to add that curve to the cowl exit before putting everything back together. Mine's going to be tough, because I have an "A" model. Doh! Lots of stuff in the way. I'm hoping it makes a big difference with oil/cht cooling.
 
Cooling

Cutting the cowl exit from the stock rearward angle to "Flush" with the firewall doesn't really open up the exit at all just reduces the lip, you have to go forward like a 20-30 degree forward angle to see much of a change in exit "area" I have found. I have also added a curved lip in the past to the bottom of the cowl exit which helps pull a little more air out. This is all on a stock cowl, but I suspect the same for a SJ cowl. The curved "Ramp" on the firewall described above helps too, but is a pain to make an effective ramp on a -A model?

Chris
 
Ideas for Cooling Improvement

I'm curious if anyone with a 7A has made a deflector scoop (like Brian)) and has any pictures to share? There is an awlful lot of stuff down there on the A models, so I am not immediately seeing how to do it.

I have a 7A with 0-360 and the long James cowl. My CHTs are acceptable, but they can get to 430 or more during leaning in summer and I'd like to get them lower. I installed louvers near the firewall (helped oil temps about 10 degrees) and have gone through and resealed the baffles very closely with a flashlight. At this point, it seems the options are A) install a deflector scoop, or B) cut back the cowl exit so that it slants forward slightly (right now it is flush). My sense is that B) is needed, as there really isn't much exit area on the A model.

Before I start cutting, I would be interested in results others have seen on the A models.


Thanks,
Scott
 
tx_jayhawk said:
I'm curious if anyone with a 7A has made a deflector scoop (like Brian)) and has any pictures to share? There is an awlful lot of stuff down there on the A models, so I am not immediately seeing how to do it.
Click to expand...

http://www.vansairforce.com/community/showthread.php?p=686477#post686477

This is not a 7a however you might can use some of the ideas from this on the way we tried to do it with a nose gear.

If you use my ideas I have one request.......you must make improvements on what I have done.:D:D:D:D

Should not be hard to do. ;)
 
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